(1) Field of the Invention
The present invention relates to the delivery of fuel to a consuming load and particularly to exercising control over the inlet pressure to a fuel pump. More specifically, this invention is directed to pressure regulators and especially to variable area jet pumps which simultaneously function as pressure control valves. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
(2) Description of the Prior Art
While not limited thereto in its utility, the present invention is particularly well suited for use in apparatus for controllably delivering a liquid to a consuming load and particularly for use in fuel controls for gas turbine type engines. Gas turbine engine fuel controls are known wherein the engine fuel inlet nozzles are coupled, by means of a fuel control, to the outlet of a gear type pump which is driven by the engine. A portion of the pressurized fuel discharged from the gear pump is not delivered to the engine but rather is fed back from the fuel control to a jet pump connected upstream of the gear pump. The passage of this pressurized fuel through the jet pump induces a flow of fuel from a supply to the gear pump inlet. In order for the gear pump to operate properly and with maximum efficiency, a predetermined inlet pressure should be maintained. In the prior art this has been accomplished by connecting a pressure control device in the feedback path between the fuel control and the jet pump, the pressure control device also preventing overpressure in the fuel control casing.
Prior attempts to make an integral jet pump-pressure control assembly have failed to provide a device having all of the necessary attributes. Thus, previously proposed pressure control-jet pump subassemblies have been characterized by one or more of a number of deficiencies. These deficiencies include large size, inefficient operation and, most importantly, the inherent operating characteristic of the jet pump not being driven by the feedback flow during those periods of time when the pressure regulator is in the open condition to relieve excess gear pump inlet pressure. Similarly, the prior art devices and systems were rendered inoperative in the case of failure, for example a valve member sticking due to particulate matter contamination, of the pressure regulator.